Tired of this mystery

[quinnwas]

Michelin Pilot on left rear wheel of my 04 330cic- <5K miles, still lots of rubber. I have a slow leak and can't collect on my warranty because two tire shops in the chain can't find a nail/screw or any other leak. They've tried tons of soapy water, full immersion to check wheel itself, soap along the rims and stem, inflation to the max, etc. Can't fault their attempts- but does anyone have an idea for what might be going on? Tire loses about a half-pound PSI per day. Any advice much appreciated-

[MarcoZandrini]

At that rate of loss you likely won’t find the leak using soapy water or even immersion. I think your best bet is to eliminate likely leaks such as the valve stem. Also, carefully inspect the alloy for hairline cracks.